Method of manufacturing bio-diesel and reactor

ABSTRACT

A reactor and process for the production of bio-diesel. The reactor includes one or more coiled reaction lines. The lines are positioned within a tank containing a heat transfer media such as molten salt, maintained at about 750° F. A pump circulates the media within the tank. An emulsion of alcohol; refined feed stock, including glycerides and/or fatty acids; and preferably water is pumped through the reaction lines at temperatures and pressures sufficient to maintain the alcohol in a super-critical state. The curvature of the coils, pump pulsing, and the flow rate of the emulsion keep the emulsion in a turbulent state while in the reactor, ensuring thorough mixing of the alcohol and feed stock. The alcohol reacts with the glycerides and fatty acids to form bio-diesel. The reaction is fast, efficient with regard to energy input and waste generation, and requires minimal alcohol.

PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No.17/075,127 which was filed on Oct. 11, 2020 and will issue on May 10,2022 as U.S. Pat. No. 10,967,354 which was a continuation of U.S.application Ser. No. 16/599,335 (U.S. Pat. No. 10,967,354) which wasfiled on Oct. 11, 2019 which was a continuation of U.S. application Ser.No. 16/252,084 (abandoned) filed on Jan. 18, 2019, which was acontinuation of U.S. application Ser. No. 15/331,586 (U.S. Pat. No.10,183,268) filed on Oct. 21, 2016, which was a continuation of U.S.application Ser. No. 14/012,810 (U.S. Pat. No. 9,475,029) filed on Aug.28, 2013, all of which are hereby incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to the production of bio-diesel in general andhigh efficiency production of bio-diesel in particular.

Prior Art

The production of bio-diesel from waste oils is known. The feed stock iscommonly comprised of glycerides and free fatty acids. Glyceridesconsist of one to three long chain fatty acids bound to a glycerolmolecule. Glycerides are often present in the form of vegetable oranimal oils or fats, such as those available as used cooking grease(fats, oils, and grease—FOG). The feed stock may also often containsoluble and insoluble impurities such as proteins, sugars, detergents,emulsifiers and degradation products of the FOGs generated during theiruse or storage.

The raw stock is usually quite viscous. In the prior art, the raw stockis commonly heated to temperatures greater than 180° F. to make the rawstock flowable and filterable. Heating the raw stock creates severalproblems. It is energy intensive, and thus expensive. It also results inthe release of volatile organic compounds (VOCs). These either must becaptured, which increases costs or they are released into theatmosphere, resulting in pollution. Heating the raw stock is alsoresponsible for the release of nuisance odors into the atmosphere. Whilenot necessarily a health hazard, the emission of these odors isunpleasant for workers and those who work or live proximate to alocation where the raw stock is being processed.

Heating the raw stock also has adverse effects on sulfur content. Sulfuris commonly present in the raw stock at levels above 0.1 percent byvolume (1000 parts per million or ppm). However, the sulfur contaminantsare typically associated with the water phase of the raw stock. Heatingthe raw stock can cause the sulfur contaminants to disassociate from thewater phase and disperse into the FOG. This can make it difficult andexpensive to achieve the 0.0015 percent by volume (15 ppm) sulfurceiling imposed by U.S. federal regulations on highway diesels and evenlower sulfur ceilings in place in other countries, particularly inEurope.

Once the raw stock is fluidized and filtered, mono-alkyl esters(bio-diesel) are formed by reacting the glycerides and free fatty acidswith alcohol, typically methanol or ethanol, in the presence ofcatalysts. A catalyst such as a strong acid (e.g. sulfuric acid) is usedto facilitate the reaction of alcohol with the free fatty acids. Theacid is then neutralized with a strong base such as sodium hydroxide.The stock/bio-diesel mixture is rinsed to remove the salts formed duringacid neutralization. Additional strong base and additional alcohol arethen added to react with the remaining glycerides to form bio-diesel andglycerol. The glycerol by-product and catalyst are separated and removedand waste water must be removed and treated as well.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a reactor that canefficiently process a wide variety of feed stocks.

It is another object of the invention to produce high quality, lowsulfur bio-diesel.

It is yet another object of the invention to produce bio-diesel withoutthe use of a supplemental catalyst.

It is still another object of the invention to produce bio-dieselefficiently.

It is yet another object of the invention to produce bio-diesel quickly.

It is still another object of the invention to minimize theenvironmental effects of producing bio-diesel.

It is yet another object of the invention to produce bio-diesel in acontinuous process.

SUMMARY OF THE INVENTION

The present invention involves the use of super-critical alcohol,preferably methanol, to react with glycerides and free fatty acids in arefined feed stock. The use of super-critical alcohol allows thereaction to proceed without a supplemental catalyst. The refined feedstock and alcohol are emulsified and forced through a reactor. Thereactor is designed to utilize heat efficiently in order to minimize theenergy needs of the system. Non-laminar, and preferably turbulent, flowis maintained throughout the reactor which effectively and thoroughlymixes the super-critical alcohol with the glycerides and fatty acids inthe emulsion. This minimizes the amount of alcohol required to completethe reaction while simultaneously reducing the amount of time requiredto complete the reaction. Waters in the emulsion are maintained atelevated temperatures and pressures, typically in the sub-critical rangefor water. This will help solubilize the glycerides in the waters,enhancing contact between the glycerides and the alcohols. The presenceof the high temperature, high pressure waters will also help break theglycerol-fatty acid bonds and inhibit dehydration of the alcohols andglycerin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a flow chart illustrating a preferred method for preparingrefined stock from raw stock.

FIG. 2A is a flow chart illustrating a preferred method of formingbio-diesel from refined stock.

FIG. 3A is a perspective view of a preferred embodiment of a heatexchanger.

FIG. 3B is a cross-section of the heat exchanger illustrated in FIG. 3A.

FIG. 4A is a perspective view of a preferred embodiment of a reactor andoverflow basin.

FIG. 4B is a side cut-away view of the reactor and basin of FIG. 4A cutalong line B-B.

FIG. 5A is a perspective view of a preferred embodiment of a shell.

FIG. 5B is an end view of a preferred embodiment of a shell.

FIG. 5C is a cut-away perspective view of a preferred embodiment of ashell, illustrating the reaction line coil within.

FIG. 5D is a detail view of a portion of 5C identified therein, with thepacking material shown in reduced quantities for illustration purposes.

FIG. 6A is a chart illustrating the chemical properties of thebio-diesel produced in Example 1.

FIG. 6B is a chart illustrating the chemical properties of thebio-diesel produced in Example 2.

FIG. 6C is a chart illustrating the chemical properties of thebio-diesel produced in Example 3.

FIG. 6D is a chart illustrating the chemical properties of thebio-diesel produced in Example 4.

FIG. 6E is a chart illustrating the chemical properties of thebio-diesel produced in Example 5.

DETAILED DESCRIPTION OF THE INVENTION

The raw stock may be any source of glycerides and/or free fatty acids.Potential sources of raw stock include used cooking oils; the fat, oil,and grease (“FOG”) from a grease interceptor or trap; and the “float”from a sewage treatment tank or lagoon—i.e., the high fat content layertypically found floating in early stage sewage treatment. The raw stockwill typically contain from about ten to eighty percent water, byvolume; about fifteen to fifty percent solid waste, by volume; and fromabout 2.5 to about fifty percent FOG by volume. As noted above, the rawstock is typically quite viscous. Although the properties of typical rawstocks are provided above, it should be noted that one of the advantagesof the present invention is its ability to work with a wide range of rawstocks.

In practice, the raw stock typically arrives by truck. The raw stock isfirst treated by passing it through a filter, preferably of about 2300microns, in order to remove the larger solids. In the preferredembodiment, an hydrophobic solvent is added to make the raw stocksufficiently flowable and filterable. Quantities of solvent may be up tofifty percent by volume of the FOG phase of the raw stock. While it isdesirable to limit the amount of solvent utilized, a sufficient amountshould be used to keep the raw stock flowing through the filter.Typically about twenty percent by volume of the FOG phase of the rawfeed stock will be sufficient to achieve the necessary fluidity.

The raw stock and solvent may be heated, but to temperatures less thanabout 120° F., and preferably to about 110° F. This avoids many of theproblems created by heating the stock to make it flowable. In systemswhere the stock is heated to achieve fluidity, venting or vapor controlsare usually required. Because most noxious components are not volatizedat the lower temperatures of the preferred embodiment, no such systemsare necessary.

Many appropriate solvents will dissolve the waste FOGs. Diesel oil is asuitable solvent, particularly when the end product is expected to beused in a diesel/bio-diesel blend. Bio-diesel is a preferred solvent asany carry-over can be included in the product regardless of the intendeduse of the end product. When the solvent needs to be separated from theend product, use of a solvent with a lower gel point than bio-dieselwill usually be preferred, as the relatively high gel point ofbio-diesel is a convenient way to effect separation.

Once fluidized the raw stock and solvent are moved to a separationvessel where they are allowed to settle, preferably for up totwenty-four hours. This will result in the formation of four distinctlayers: a layer of solids less than 2300 microns on the bottom; a clearwater phase commingled with the solids and typically extending above it,depending upon volume; an emulsion phase located above the water phase;and an FOG/solvent phase at the upper layer.

The upper FOG/solvent layer is pumped off and stored. If desired tofacilitate pumping or any other reason, the height of the upperFOG/solvent layer may by raised by adding water.

The remaining layers are passed through a 1200 micron filter to removethe majority of the remaining manmade solids. The filtrate is preferablythen centrifuged. In the preferred embodiment, the filtrate is firstpassed through a decanter centrifuge to remove the majority of solidsgreater than twenty microns in diameter and then through a disc stackcentrifuge to remove the majority of solids greater than five microns indiameter. The disc stack centrifuge will also separate the emulsionlayer into an hydrophobic layer and a hydrophillic and water layer. Thehydrophobic layer will be less than ten percent water by volume.

The hydrophillic components and waters are separated and treated forreintroduction into the process, use in other processes, as appropriateor eventual discharge into a municipal sewage system or other suitablereceiving body.

The hydrophobic layer is tested for sulfur content. If the sulfurcontent of the hydrophobic layer exceeds 1000 ppm remediation is inorder. Depending upon the chemistry of the hydrophobic layer, it may betreated with an acid solution having a pH of about 3.0 or below or abasic solution with a pH of about 13.0 or above to separate contaminantfunctional groups from fatty acid backbones. After separation, the fattyacid backbones may be returned to the feed stock for processing intobio-diesel; or the hydrophobic layer may be diverted for use in anotherprocess. However, it will be noted that the hydrophobic layer typicallycomprises only about one to two percent by volume of the raw feed stock.Many of the sulfur contaminants are often present in this layer.Accordingly, it often makes sense to discard this layer or to divert itfor use in another process rather than attempting to remediate andprocess into bio-diesel the FOG and glycerides it may contain.

The upper FOG/solvent layer is passed through the same filtration andcentrifuge steps discussed above in order to remove solids above fivemicrons and to reduce the water content below about ten percent byvolume.

The raw stock/solvent may be warmed slightly to enhance flowability.However, in all of the foregoing filtration and centrifuge steps, thetemperature is preferably maintained below about 120° F. and preferablyat about a F. It will be appreciated that many of the water solublesulfur contaminants present in the raw stock will be removed with thewaters as the lower temperatures of the preferred process will result infewer of the sulfur contaminants becoming disassociated from the waters.

The filtered and centrifuged FOG/solvent layer will be combined with thehydrophobic component that was separated from the emulsion layer,assuming that either the hydrophobic component did not contain excessiveamounts of sulfur or that it was treated. At this stage, the mixtureshould preferably be about 2.5 percent or less solids, by volume, withthe solids having a diameter of about 5 microns or smaller Water shouldcomprise about ten percent by volume or less. More than abouteighty-five percent by volume, and preferably more than abouteighty-seven percent by volume should be glycerides, free fatty acids,and solvent. In addition, there will be relatively small amounts (lessthan about 0.05 percent and most preferably less than about 0.01percent, by volume (less than about 500 ppm and most preferably lessthan about 100 ppm)) of other lipids (e.g., sphingolipids, glycolipids,and phospholipids); detergents (e.g., long chain fatty alcohols, alcoholethoxylates and alcohol ethoxysulfates (AES) and organosulfates); andsurfactants. Stock meeting these criteria is referred to as refined feedstock. It should be understood that refined feed stock may be obtainedfrom a raw stock in the manner described above or it may be obtained ina form that already satisfies these conditions. Examples of stock thatqualifies as refined feed stock would include used cooking oils andunrefined fats, oils and greases of animal or plant origin filtered toremove solids greater than 5 microns in size.

The refined feed stock is next mixed with alcohol, preferably methanol,though other alcohols may be used. Suitable alcohols will have acritical point below 650° F. and 2500 psig. Linear and branched alcoholshaving chains of up to five carbons are expected to be suitable.Examples include ethanol, propanol, butanol, and pentanol. Theappropriate molar ratio ranges from about 3:1 to 15:1 alcohol toglycerides in the refined feed stock, and preferably about 9:1 to 12:1.In practice, the alcohol levels will simply be reduced as low aspossible while still obtaining, preferably in one pass, substantiallycomplete conversion of the glycerides and free fatty acids to mono-alkylesters. This may be verified by using gas chromatography to analyze therefined feed stock and the finished product. Gas chromatography or othersuitable analytic methods will provide the molar content of theglycerides and free fatty acids in the feed stock and confirm thatsubstantially all of the glycerides and free fatty acids have beenconverted to mono-alkyl esters. Examples are provided below.

It will be appreciated that the highest alcohol demands will beencountered in refined feed stocks having the highest triglyceridecontent. Vegetable oils are an example of such a refined feed stock.Triglycerides require more alcohol on a molar basis because each of thethree fatty acid chains must be reacted with a separate alcohol moleculein order to achieve complete esterification. That is, one mole oftriglyceride will release three moles of fatty acid, each of which mustbe reacted with a mole of alcohol. Refined feeds stocks that comprise agreater percentage of mono- and di-glycerides will requireproportionally less alcohol to complete esterification. In view of theforegoing, it will be appreciated that the molar ratio necessary tocompletely esterify a refined feed stock whose fatty acids aresubstantially all in the form of triglycerides represents the maximumamount of alcohol expected to be required. The inventors have determinedthat a 15:1 molar ratio of alcohol to glyceride is sufficient tosubstantially complete esterification of a refined feed stock whoseglycerides are substantially all in the form of triglycerides, e.g.,refined and deodorized vegetable oils and animal fats. Lower molarratios will be suitable for refined feed stocks whose glyceride contentis more varied.

When there are substantially no glycerides present in the refined feedstock, that is when the fatty acids are present as free fatty acids,obviously it does not make sense to speak of a ratio of moles of alcoholto moles of glyceride. Here the relevant ratio is moles of alcohol tomoles of fatty acid. In this context, only one mole of alcohol will beneeded to react with each mole of free fatty acid. Although some excessalcohol is required to ensure that the reaction proceeds expeditiously,molar ratios of as low as 3:1 (alcohol to fatty acid) are suitable.

Regardless of the source of the fatty acids—whether they are present inand must be freed from a glyceride molecule or if they are present asfree fatty acids in vegetable oil or the like—the alcohol requirementsby weight are relatively small. To achieve the necessary molar ratios,alcohol in the amount of about seven to about twenty-one percent byweight of the emulsion exiting the mixer will be adequate for mostrefined stocks. In the majority of cases, alcohol between about twelveand about sixteen percent by weight of the emulsion will suffice.

The alcohol and refined feed stock are preferably mixed using meteringpumps 102, most preferably one for the alcohol and one for the refinedfeed stock. This allows the target amount of alcohol to be used, therebyensuring that sufficient alcohol is present for both the desiredreaction and the formation of the desired emulsion while avoiding theunnecessary addition of excess alcohol. Suitable metering pumps includepositive displacement diaphragm pumps such as those available from DXPEnterprises of New Orleans, Louisiana.

The mass of the feed stock will vary depending upon the amount of waterpresent, the amount of glycerides present, and the amount of solventpresent as well as the nature of the solvent. A refined feed stockcomprised of about fourteen to about twenty-seven percent solvent byweight of the emulsion exiting the mixer is preferred, and mostpreferably about twenty to about twenty-two percent solvent by weight.Typical density of the preferred feed stock can be expected to be about500 gm/ml. Densities above about 600 gm/ml, particularly when the watercontent of the feed stock is low (below about two percent by volume), isindicative of higher amounts of triglycerides and/or diglycerides andsuggests a need for greater amounts of alcohol. A water-in-oil meter ispreferably used to determine the amount of water present in the feedstock. Suitable meters include the in-line meters available from EESiFloNorth America of Mechanicsburg, Pennsylvania A mass flow meter ispreferably used to determine the mass of the feed stock. Suitable metersinclude the in-line mass flow meters available from Yokogawa of NorthAmerica of Houston, Texas. The output of these meters is used to adjustmetering pumps 102 for the alcohol and/or the refined feed stock toobtain the desired molar ratio.

After the desired feed stock and alcohol ratios are established, thealcohol and feed stock mixture is preferably passed through one or moremixers 103, preferably an in-line high shear mixer. Suitable high shearmixers include the Greerco Inline Pipe High Shear Mixer available fromChemineer, a division of Robbins & Meyers, Inc. of Willis, Texas. Thealcohol and feed stock should exit the high shear mixer as a stableemulsion with an average droplet diameter on the order of 1×10-7 to 10-8m.

The emulsion is preferably passed through a mass flow meter to confirmthe emulsion's stability. Suitable mass flow meters include the Coriolisin-line mass flow meter available from Yokogawa of North America,headquartered in Houston, Texas. The mass flow meter will ideallyindicate a density of about 1.0 kg/1±0.5 kg/l.

The emulsion will typically be at or near ambient temperature andpressure. It is next heated and pressurized. Either step may occurfirst; however, in the preferred embodiment the emulsion is pressurizedfirst. In the preferred embodiment, the emulsion is passed through oneor more pumps 105, preferably a high pressure piston pump, such as theHydra Cell pump available from Wanner Engineering, Inc. of Minneapolis,Minnesota. The pressurized emulsion should preferably be between about2000 and 3000 pounds per square inch gauge (psig), and most preferablyabout 2500 psig.

The emulsion is passed through one or more heat exchangers 106. Heatexchangers 106 are preferably shell and tube exchangers, preferablyembodying a single pass shell, countercurrent flow design. Materials andconstruction techniques for heat exchangers 106 should be selected sothat heat exchangers 106 will be substantially chemically inert to theemulsion under the desired heat transfer conditions and so that heatexchangers 106 can withstand the anticipated temperatures and pressuresto which heat exchangers 106 will be subject. Although shell and tubedesigns are expected to be sufficient to achieve the thermal objectivesin the preferred application, other heat exchanger designs, such asspiral or plate heat exchangers may be utilized according to the heattransfer need specific to the application. Additionally, heat exchangers106 may be provided with fins or other obstructive elements to enhanceheat transfer between the two flows. Heat exchangers suitable for use inthe preferred embodiment may be obtained from Tranter, Inc. of Wichita,Falls, Texas.

Exiting heat exchanger 106, the emulsion should preferably be betweenabout 550° to 620° F. and most preferably at about 600° F. The pressurewill be relatively unchanged. In one preferred embodiment, multiple heatexchangers 106 are provided. One or more are provided outside of reactor200 (discussed below) and at least one heat exchanger 106 is positionedinside reactor 200, or more preferably inside reactor reservoir 209. Inthis embodiment, the emulsion exits the heat exchangers 106 external toreactor 200 between about 440° and 460° F. and most preferably at about450° F. The pressurized emulsion is then passed through the heatexchanger 106 positioned inside reactor reservoir 209. The emulsion willexit the internal heat exchanger 106 between about 550° and 620° F. andmost preferably at about 600° F. The pressure will be relativelyunchanged. By utilizing the heat exchanger 106 contained in reservoir209, the emulsion may be efficiently brought to the desired reactiontemperature immediately prior to entering reactor 200.

It will be appreciated that at these temperatures and pressures, thealcohol will be supercritical (i.e., above the critical point), thewater will be sub-critical (i.e., above the atmospheric boiling pointbut below the critical pressure and temperature of 3210 psig and 705°F.). However, the entire emulsion is believed to behave as a homogenous,super-critical fluid, as discussed in more detail below.

The now pressurized and heated emulsion will enter the reactor 200.Reactor 200 is comprised of one or more shells 201, preferably tubularin shape and most preferably configured in the approximate shape of aring torus. Shells 201 are preferably constructed from thermo-conductivematerials such as silicon carbide, carbon steel or other steel alloys.The material for shell 201 should be substantially chemically andphysically inert to heat transfer media 215 under the expected operatingconditions of reactor 200 and it should be physically strong enough tosustain and direct the burst pressure from reaction line 20 (discussedbelow) in the event of a reaction line failure. In the preferredembodiment, shell 201 is comprised of ABS A-grade carbon steel with awall thickness of about 0.25 inches.

Inside each shell 201 is a reaction line 202 through which thepressurized and heated emulsion travels. Reaction lines 202 arepreferably configured in the shape of a coil 203. Reaction lines 202should resist corrosion by the materials contained within them andshould be physically strong enough to withstand the pressure theemulsion is under. A three to one safety ratio is preferred, meaningthat reaction lines 202 should be comprised of materials of sufficientthickness and strength to withstand three times the amount of force towhich reaction lines 202 are expected to be exposed. The particularcomposition of reaction line 202 will depend upon the nature of theemulsion and the conditions at which reactor 200 is operated. In apreferred embodiment, reaction line 202 is comprised of 316 stainlesssteel tubing having an outside diameter of about one half inch, a wallthickness of about 0.065 inches, and an inside diameter of about 0.37inches.

In sizing reaction line 202, several objectives should be kept in mind.The pressure to which the emulsion will be subjected will effect theminimum thickness of reaction line 202. The walls of reaction line 202must be strong enough to withstand the pressure applied to the emulsiontraveling through line 202. All other things being equal, that meansthat greater pressures require thicker walls. Stated differently, atconstant pressure a pipe with a smaller inside diameter requires thinnerwalls than a pipe with a greater inside diameter. Thus, increasing theinside diameter requires the walls of reaction line 202 to increase inthickness, if reaction line 202 is to withstand the pressures commonwithin the preferred embodiment of reactor 200. All other things beingequal, pipe with thinner walls will generally be less expensive and willtransfer heat more readily than pipe with thicker walls.

There are costs to using smaller, thinner pipe, though. The smallerinside diameter pipe will carry less fluid at any one time than the samelength of pipe with a larger inside diameter. As a result, at constantpressure, the fluid in the smaller inside diameter pipe will move fasterthan the fluid in the larger inside diameter pipe. If retention time isan issue and pressure is kept constant, greater lengths of small insidediameter pipe must be used to achieve the same retention time as shorterlengths of large inside diameter pipe. Thus, if pressure must be keptconstant and the pipe contents must be maintained in the reactor for arequisite amount of time, a greater length of small inside diameterreaction line 202 will be required than if larger inside diameter pipeis used for reaction line 202.

In the preferred embodiment, each reaction line 202 comprises a coil 203that includes multiple turns 204 running within and preferably along thebottom of torus shaped shell 201. In one preferred embodiment, a coil203 comprises thirty-eight turns 204 about a radius ranging fromeighteen to fifty-eight inches and has a length of 350 feet. Although inthe preferred embodiment, each shell 201 includes only one reaction line202, multiple reaction lines 202 could be included within a shell 201.

The space between shell 201 and reaction line 202 is preferably filledwith chemically inert packing material 205. The optimal thermalconductivity of packing material 205 will depend upon the thermalconductivity of heat transfer media 215 (discussed below) and of shell201. Packing material 205 should preferably have a lesser thermalconductivity than that of heat transfer media 215 and a greater thermalconductivity than shell 201. This will facilitate heat transfer acrossshell 201. In the preferred embodiment, packing material 205 will have athermal conductivity at least about 200 BTU/ft h F.

Packing material 205 also acts as a dampener to suppress the hammereffect on reaction line 202 caused by pump 105 moving the emulsionthrough reaction line 202. In the preferred embodiment, the packingmaterial is silicon carbide. Other suitable packing materials includesand or glass, depending upon intended reaction conditions. In order toprevent clogging of the safety valves or burst disks in shell 201, it ispreferable that the packing material have a particle size of less than200 microns. In the preferred embodiment, packing material 205 is 120grit/125 micron in size with a density of 89 lbs/ft3 (1.43 g/cc). Thepacking material 205 is typically heated in situ to remove moisture. Avacuum is then applied to ensure tight packing, maximizing contactwithin packing material 205 which aides in thermal conductivity.

Multiple shells 201 may be provided by stacking them within reactor 200.A framework is provided to support each shell 201 within reactor 200.The framework should position shells 201 so that they are separated fromeach other, preferably by at least about three inches. In the preferredembodiment, the framework will also serve as cross braces for tank 208.Preferably, the framework should be made of the same material as tank208.

When multiple reaction lines 202 are present, they are fluidlyconnected. In the preferred embodiment, the pressurized emulsion flowsinto one end of reaction line 202, preferably passing through the wallof shell 201 and out the opposite end of reaction line 202, againpreferably passing through the wall of shell 201. In the preferredembodiment, the outflow from reaction line 202 is connected to amanifold 207 comprising a plurality of valves. Manifold 207 may beconfigured to direct the outflow of one reaction line 202 into theinflow of the next reaction line 202 so that the emulsion may be passedthrough multiple shells 201 and reaction lines 202 in succession.Alternatively, the manifold 207 may direct the outflow of any reactionline 202 out of reactor 200, whereby the outflow will become theeffluent from reactor 200.

Manifold 207 is preferably positioned exterior to tank 208 (discussedbelow). Manifold 207 should preferably be provided with a plurality ofsensors configured to continuously measure pressure, temperature andmass flow as the fluid enters and exits each reaction line 202 and/orshell 201. Suitable sensors are available from Thermal Solutions ofHouston, Texas. The data gathered by the sensors is transmitted to acomputerized control system so that the operator and/or a computerizedoperations program may monitor the operation of reactor 200.

The number of reaction lines 202 through which the emulsion passes maybe selected by the operator and will depend upon the desired holdingtime for the emulsion within reactor 200. However, the longer reactionline 202, the greater the drop in pressure across line 202. Both thefriction between the inner wall of reaction line 202 and the continuousangular velocity imparted to the emulsion by the curvature of coils 203will result in loss of pressure in lines 202. Although some pressureloss is unavoidable, sufficient pressure must be maintained to keep thealcohol in the emulsion in a super-critical state. Likewise, water inthe emulsion should not be allowed to boil.

One step that can be taken to minimize pressure losses in reactor 200 isto enlarge the inside diameter of lines 202; however, that has costs, asdiscussed above. Another step that can be taken is to enlarge in theinside diameter of the connecting lines between reaction lines 202. Thiswill reduce the additional pressure losses that occur in reactor 200external to lines 202. If the inside diameter of the connecting lines isincreased, the connecting lines should preferably have an internaldiameter that is greater than the internal diameter of reaction lines202 by at least about twenty-five percent, but not more than aboutseventy-five percent.

Shell(s) 201 are contained within tank 208. Tank 208 is preferably madeof carbon steel and is generally cylindrical with a thickness of aboutthree quarters of an inch. Tank 208 is preferably open ended and restson and within a reservoir 209, also preferably made of steel. In thepreferred embodiment, a heat exchanger 106 is provided in reservoir 209.

In the preferred embodiment, reservoir 209 sits upon a grated platform210 covering an overflow basin 211. Basin 211 should preferably be ofsufficient size to contain the entire volume of tank 208 and reservoir209. It will be appreciated that in the event of a failure of tank 208,reservoir 209, or any of the other components of reactor 200, thecontents of the same may be directed to and captured in basin 211.Reservoir 209 is also preferably provided with a valve that will allowthe contents of tank 208 to be discharged into basin 211.

The top of tank 208 is provided with a fluid tight lid 212. Lid 212 isalso preferably made of steel and is bolted to the top of tank 208. Inthe preferred embodiment, a high temperature, chemically inert, metallicgasket, preferably made of hydrous aluminum silicate available fromDeacon Industries of Washington, Pennsylvania, is provided between tank208 and lid 212 to ensure a seal between lid 212 and tank 208.Chemically inert, heat compatible metallic gaskets constructed fromsteel and/or steel alloys may also be used.

One or more heaters 213 are positioned within tank 208. Heater 213 ispreferably an electric flange heater such as those available fromThermal Solutions of Houston, Texas. Heater 213 is preferably providedwith separate circuitry which may be powered independently. This 10 willallow heater 213 to be operated from about ten percent capacity to onehundred percent capacity, avoiding the “all on/all off” pulsing commonin conventional heaters.

In the preferred embodiment, heater 213 is contained within a perforatedpipe 214. Pipe 214 is preferably made of the same material as tank 208.In the preferred embodiment, pipe 214 and heater 213 are verticallyoriented within tank 208. When shells 201 are torus shaped, pipe 214 andheater 213 will preferably be positioned within shells 201 in alignmentwith the axis of the torus. It will be appreciated that in thisconfiguration, shells 201 surround pipe 214 and heater 213 and may bepositioned so that all portions of each shell 201 are roughlyequidistant from heater 213.

Tank 208 is partially filled with a heat transfer media 215. Heattransfer media 215 should be selected to effectively transfer heatthroughout tank 208. As discussed above, heat transfer media 215 shouldhave thermal conductivity that is greater than that of packing material205 and most of the other components of reactor 200 separating heattransfer media 215 from the contents of reaction line 202.

Heat transfer media 215 will heat packing material 205 across shell 201.As discussed below, heat transfer media 215 is preferably liquid whilepacking material is 205 preferably solid and shell 201 is also solid.Thus, convection will be the main heat transfer mechanism from heattransfer media 215 to the outer surface of shell 201. Conduction will bethe predominant heat transfer mechanism from the outer surface of shell201, through packing material 205, to the outer surface of reaction line202.

The higher the thermal conductivity of a material, the better it willtransfer heat to a cooler material. To efficiently transfer heat throughreactor 200, heat transfer media 215 should have a thermal conductivitythat is greater than that of shell 201 and packing material 205.Similarly, the thermal conductivity of packing material 205 should begreater than that of shell 201 and reaction lines 202. This will helpprevent shell 201 from acting as a heat barrier. Rather, heat will flowfrom heat transfer media 215, across shell 201, through packing material205 to reaction line 202.

In the preferred embodiment, heat transfer media 215 should preferablyhave a thermal conductivity value of between about 800 and about 2900BTU/ft2 h F. This can be compared to the preferred thermal conductivityof shell 201, which has a thermal conductivity of about 20 BTU/ft2 h F,packing material 205 which has a thermal conductivity of about 200BTU/ft2 h F and the thermal conductivity of the preferred material forreaction lines 202, about 20 BTU/ft2 h F.

The preferred heat transfer media 215 includes a molten eutectic mixtureof water soluble, inorganic salts of potassium nitrate, sodium nitriteand sodium nitrate available from Coastal Chemical Company of Abbeville,La, under the brand name Hitec. In operation, when the heat transfermedia is molten salt, it will preferably be maintained between about650° and 775° F. and most preferably at about 750° F.

Heat transfer media 215 should be filled to a level (L) above thehighest shell 201, so that all shells 201 are immersed in heat transfermedia 215. In the preferred embodiment, heat transfer media 215 extendsfrom level L to the bottom of tank 208 and into reservoir 209. Level Land heater 213 are preferably positioned relative to each other so thatthe entire active portion of heater 213 is positioned within heattransfer media 215 and the inactive portions are positioned above levelL.

One or more circulation pumps 216 are provided to circulate transfermedia 215. Circulation pump 216 is preferably positioned adjacent totank 208. Pump 216 should have an inflow line positioned below level L,and preferably at least about fifteen percent of the height of L belowlevel L, to ensure that pump 216 is able to maintain suction with heattransfer media 215. Pump 216 should have a discharge line 219 configuredto discharge into pipe 214 so that the re-circulated transfer media 215flows directly over the coils of heater 213. Suitable circulation pumps216 include a molten metal vertical pump such as those available fromGusher Pumps of Williamstown, Kentucky (USA).

A secondary fill line may be provided. The secondary fill line wouldpass through tank 208 and open into pipe 214. Heat transfer media 215may be provided through the secondary fill line, particularly atstart-up. This will de-gas the area surrounding the coils of heater 213by filling it with liquid, thereby protecting the coils and moreeffectively transferring heat from heater 213 to the surrounding media215, which may be solid at start up.

In addition or in the alternative, a circulation manifold may beprovided to direct the effluent of pump(s) 216 proximate to particularshells 201, as desired. Tank 208 may also be provided with one or moreexternal heaters 221. In the preferred embodiment, external heaters 221are band heaters positioned on the outside of tank 208. Suitable bandheaters include those available from Thermal Solutions of Houston, TexasExternal heaters 221 are particularly useful during startup, when heattransfer media 215 may be solid. External heaters may be used to liquefyheat transfer media 215 from the outer edge of tank 208. It will beappreciated that if transfer media 215 has been allowed to solidify, airis likely to be trapped within transfer media 215. Heating heat transfermedia 215 from the outer edge will cause the portions of transfer media215 nearest the walls of tank 208 to liquefy first, thereby creating avertical passage adjacent the walls of tank 208. This will tend tode-gas heat transfer media 215. Tank 208 and reservoir 209 arepreferably enclosed in insulation, such as four inch calcium silicateavailable from Industrial Alliance Services of Houma, Louisiana.

It will be appreciated that reservoir 209 will contain excess heattransfer media 215 which will serve as a heat battery. Once the fullvolume of heat transfer media 215 is heated to the desired temperaturerange, having a larger volume of media 215 available will prevent theoverall temperature of media 215 from falling as much as a result of theheating of the emulsion. This will allow heater 213 and/or externalheaters 221 to be used less often and/or at lower power levels thanwould otherwise be required. Reservoir 209 has a volume that ispreferably at least about twenty-five percent the volume of tank 208 andmay be larger depending upon the desired flow rate of the emulsion.

Heat transfer media 215 and reaction lines 202 are in thermalcommunication. In the preferred embodiment, heat transfer media 215 andpacking material 205 ensure that thermal energy is efficiently deliveredto reaction lines 202. This will facilitate the reaction between thealcohol and the fatty acids and glycerides in the emulsion, ultimatelyallowing esterification and transesterification to proceed more rapidlyand with less alcohol per mole of glyceride.

Reactor 200 is preferably provided with several safety components. Aburst disk is preferably provided in the upper end of tank 208, in orproximate to lid 212. The burst disk is fluidly connected to a dischargeline configured to discharge into basin 211. Should pressure in tank 208exceed the desired safety margin, the burst disk will allow the contentsof tank 208 to flow into basin 211.

Manifold 207 is preferably provided with an isolation valve for eachshell 201. In the event that a pressure increase is detected in anyreaction line 202, which could indicate a blockage, or a sharp pressuredrop, which could indicate a rupture, fluid flow through all reactionlines 202 in a shell 201 may be stopped and rerouted to the nextreaction line 202 in an adjacent shell 201. Each reaction line 202 ispreferably provided with a burst disk or safety valve fluidly connectedto a discharge line. The discharge line is configured to discharge intobasin 211. In the event that the isolation valve for any reaction line202 is closed, the safety valve or burst disk should be opened, eitherautomatically or manually, whereby the contents of the isolated reactionline may be emptied into basin 211.

Each shell 201 is preferably fitted with a burst disk. Each burst diskis fluidly connected to a discharge line configured to discharge intobasin 211. Should pressure in shell 201 exceed the desired safetylevels, the burst disk will allow the contents of shell 201 to flow intobasin 211.

The various burst disks are preferably configured to open at pressuresabout twenty-five percent above the anticipated operational pressure oftheir respective vessels. In the preferred embodiment, all vessels(e.g., tank 208, reaction lines 202, shells 201, etc.) should beconstructed to withstand pressures at least three times the anticipatedburst pressures of their respective burst disks.

It will be appreciated that shells 201 are essentially safety devices.Reaction lines 202 could be immersed directly in heat transfer media 215and the emulsion would be heated to/maintained at the desiredtemperature more readily than if heat is forced to flow across shell 201and packing material 205. However, the emulsion is under very highpressure and its contents are flammable. Additionally, the preferredheat transfer media 215 is a strong oxidizer. If reaction lines 202 werein direct contact with heat transfer media 215, the risk of failure ofreaction lines 202 would increase while the potential consequence ofsuch a failure—the emulsion being ejected under very high pressuredirectly into molten salts—would be enhanced. By positioning reactionlines 202 within shell 201, heat transfer to the emulsion is madesomewhat more difficult, but the risk of a failure of lines 202 isreduced and the potential consequences of such a failure are minimizedinsofar as shell 201 may temporarily contain any leak while reactor 200is shut down and/or flow is diverted to another shell 201/reaction line202 via manifold 207. It is also for safety reasons that the preferreddesign of shell 201 has a shape that approximates a torus. With few orno crevices or corners, shell 201 is better able to distribute and,thus, withstand any pressure spikes that may occur in the event of afailure of reaction line 202.

In operation, pump or pumps 105 drive the emulsion through reactionlines 202 of reactor 200. The preferred flow rate is maintained at orabove 18 l/min. This flow rate is sufficient to ensure a steady flowrate throughout reaction lines 202. The continuous circular motion ofthe emulsion through coil shaped reaction lines 202 and the pulsingforce from pumps 105 will ensure that the flow through lines 202 remainsat least non-laminar, and preferably turbulent, which will ensurecontinuous mixing of the alcohols with the fatty acids and glycerides inthe emulsion.

As noted above, the alcohols in the emulsion will be super-critical.Super-critical alcohols are known to effectively convert glycerides(including triglycerides) and free fatty acids to esters rapidly andwithout the need for a catalyst. It is believed that the hydrogen bondenergy is lowered under super-critical conditions, effectively allowingthe alcohol to behave like a free monomer. It is believed that underthese conditions the alcohol molecule can directly attack the carbonylcarbon of the triglyceride.

Keeping the alcohol at super-critical conditions will also significantlyenhance the ability of the alcohol to physically contact the fatty acidsand glycerides in the emulsion. Super-critical fluids have theproperties of a gas and a liquid. Thus, the super-critical alcohol willbe able to effuse through the other components in the emulsion like agas. However, the super-critical alcohol will be relatively dense ascompared to gaseous alcohol. As a result, the physical collision ratebetween the alcohol and the emulsion components will be high. Both ofthe foregoing characteristics will result in the alcohol readily cominginto contact with the glycerides.

The ability of the super critical alcohol to physically encounter andreact with the glycerides and free fatty acids in the emulsion will besignificantly enhanced by the non-laminar, and preferably turbulent,flow of the emulsion through reaction lines 202. The non-laminar flow ofthe emulsion in combination with the super-critical alcohol results inthorough mixing and promotes a more rapid, efficient and completereaction, facilitating completion of the reaction in a single passthrough reactor 200.

In the preferred embodiment, one or more back pressure control valves350 are provided in manifold 207. The back pressure control valve 350should be set at about 2500 psig. Essentially, back pressure controlvalve 350 will check the flow through reactor 200 if the pressure shouldfall below 2500 psig. This will cause the pressure to build until backpressure control valve 350 opens, allowing flow through reactor 200 toresume. It will be appreciated that back pressure control valve 350 willcontrol for the pressure drop across reaction lines 202. This willmaintain the pressure within reaction lines 202 at a sufficient level tokeep the alcohols in the emulsion in a super-critical state.

At the preferred pressure and temperature, as noted above, the water inthe emulsion is sub-critical, meaning above its atmospheric boilingpoint and below its critical point, but under sufficient pressure toprevent the water from vaporizing. Several things happen to such hightemperature water. The water molecules become less polar, making thewater a much more effective organic solvent. Because of the decrease inpolarity and also because of the elevated temperature, many oils,including the glycerides and fatty acids in the feed stock, becomesoluble in water under these conditions.

Water at very high pressure and temperature also includes several ordersof magnitude more hydronium (H3O+) and hydroxide (OH−) ions than doeswater under ambient conditions. This will give the water the propertiesof both an acid and a base. Thus, the high temperature water can performthe role of the catalyst in breaking the glycerides into free fattyacids and glycerine. High pressure, high temperature water also inhibitsthe dehydration of the alcohol and glycerin. The emulsion willfrequently contain dissolved impurities such as trace metals. Thesemetals can serve as catalysts to break the alcohols into dimethyl ether,an extremely flammable gas. Similarly, the metals can serve as catalyststo break glycerin into acrolein, a highly toxic chemical. In thepreferred range of temperature and pressure, the water can form ioniccomplexes with the metals that can inhibit the catalytic activity oftrace metals, thereby preserving the alcohol and glycerin.

The waters in the emulsion are necessarily maintained at the samepressure and temperature as the alcohols and other emulsion components.These pressures and temperatures are sufficient to optimize theadvantages discussed above.

Although the reaction can proceed without any water, water between theamount of about five and about twenty percent by weight of the emulsionand most preferably about ten to fifteen percent by weight of theemulsion will allow the reaction to proceed more quickly and morecompletely with less alcohol and fewer undesired side reactions andby-products. Water content approaching the fifteen percent range andhigher complicates the isolation of alcohol from the finished productfor recycling. Thus, keeping the water content of the emulsion at aboutten percent by weight of the emulsion is most preferable.

There is some uncertainty as to how to characterize the water in theemulsion under the preferred conditions. On the one hand, the waterswill be between the boiling point of water and the critical point ofwater. Such waters can be reasonably characterized as sub-critical.However, the alcohols in the emulsion will clearly be super-criticalunder the preferred conditions. The volume of the alcohol will be atleast three to four times that of the water present. As a result, it isbelieved that the physical state of the alcohol predominates.

Observation of the fluid during operation of reactor 200 indicates thatthe emulsion is behaving as a homogenous, super-critical body. This isconsistent with the expected effect of a substantial quantity ofsuper-critical alcohol in a thoroughly mixed and turbulent emulsion,namely homogenization of the entire fluid body. Thus, the entireemulsion is believed to behave like a super-critical fluid while inreactor 200. All of the foregoing will facilitate bringing the alcoholsand catalytic waters together with the glycerides and fatty acids,accelerating both the breakdown of the glycerides and fatty acids intofree fatty acids and the formation of bio-diesel. The reaction willproceed more quickly and less excess alcohol will be required to ensurethe reaction proceeds to completion.

Overexposure to the high temperature and pressure of the reactionconditions can have adverse effects on fuel quality and viscosity.Primarily, this is the result of polymerization of polyunsaturated fattyacids from the cis form to the trans form. One way to ameliorate thisrisk is to operate at lower temperatures over longer periods. However,this is energy intensive and relatively expensive. A more efficient wayto moderate this risk is to remove the emulsion from the reactor as soonas the reaction is substantially complete. By monitoring the state ofthe reaction with Coriolis mass flow meters, and utilizing manifold 207,the emulsion may be removed from reactor 200 as soon as the reaction iscomplete. For example, with the refined feedstock described in exampleno. 1, whose FOG's are primarily triglycerides, a drop in density ofabout 1 lb/ft3 will indicate that the reaction is substantiallycomplete.

Removing the emulsion from reactor 200 promptly upon completion of thereaction will minimize excess holding times under reaction levelconditions. It will be appreciated that this is a particular concernwhen the quality of the feed stock is inconsistent. The amount of excesspolyunsaturated fatty acids in the FOG's, particularly the amount oflinoleic acid and linolenic acid, will effect how long the refined feedstock needs to be maintained under reaction conditions.

In the preferred embodiment, the emulsion should remain between about560° and 620° F. and most preferably at about 590° F. under non-laminar,and most preferably turbulent, conditions for between about 1.5 andabout 5.5 minutes and most preferably about four minutes. In thepreferred embodiment, this is accomplished by passing the emulsionthrough about 3000 feet (915 meters) of reaction line 202 at a flow rateof about 10 feet/second (3.0 meters/second), all while maintaining thereaction lines 202, inside shells 201, in a circulating bath of 750° F.molten salt.

One potential problem for any reactive system including oils in contactwith high temperature metals is coking. Carbon deposits can form from(incomplete) combustion of the oils or, in substantially oxygen freeenvironments such as that inside reactor 200, from pyrolysis of theoils. Either process can result in the deposit of carbon on the metalsurface, which can clog lines and valves and generally have adeleterious effect on the process. However, no such coking has beenobserved in the operation of reactor 200. It is believed that the watersin the emulsion, the homogenous super-critical nature of the fluid, andthe non-laminar and preferably turbulent flow of the emulsion throughreactor 200 prevent or substantially inhibit coking. In particular, itis believed that the non-laminar flow and the homogenous super-criticalnature of the fluid disperse the waters evenly throughout the emulsion.This is believed to make the greater potential heat capacitance of thewaters available to absorb heat from reaction line 202, therebyshielding the oils to some degree. Furthermore, to the extent that anypyrolysis does occur, the non-laminar flow is believed to scour reactionlines 202, preventing any substantial build up of coke.

Upon exiting reactor 200, the effluent will be comprised of bio-diesel,solvent (which may be bio-diesel), glycerol, alcohol, water, andcontaminants. The effluent will be about 600° F. If the efficiency ofthe process is to be maximized, it is important that the heat from thiseffluent be utilized. That can be done by recycling the heat to warm theemulsion entering reactor 200 or to drive the separation of the effluentcomponents. In the preferred embodiment, the heat of the effluent isused for both purposes.

In one embodiment, the pressure is released from the effluent stream,preferably immediately prior to or contemporaneously with entry of theeffluent stream into a distillation column 300. A back pressure controlvalve 350, such as those available from Schubert & Salzer of Concord,North Carolina, is preferably used to return the effluent stream toambient pressure. As discussed above, similar back pressure controlvalves 350 may be utilized at manifold 207 to maintain pressure.

It will be appreciated that upon the removal of pressure, essentiallyall of the alcohol and water will boil out of the 600° F. effluentstream. Most of the contaminants, including especially the organicsulfur containing contaminants, have a boiling point below 450° F. Forexample, some of the more common sulfur contaminants still present wheneffluent exits reactor 200 include disulfides and thiols, which haveboiling points around 150° F. or less. Thus, most of the organic sulfurcontaminants present in the effluent will boil out in first distillationcolumn 300. The light effluent from distillation column 300 will includethe alcohol, water and contaminants. The light effluent will be passedthrough a second distillation column 301, where the alcohol will beboiled out, captured, and recycled for further use in bio-dieselrefining. The 20 water and remaining contaminants, most if not all ofwhich will be water soluble, will be collected and treated, either onsite or at an off site water treatment facility.

Suitable distillation columns 300 and 301 are available from SulzerChemtech of Tulsa, Oklahoma. It will be appreciated that heat may beadded to distillation columns 300 and 301 as necessary.

The heavy effluent of distillation column 300, though at atmosphericpressure, will still be at about 450° F. The heavy effluent will bepassed through one or more heat exchangers 106 in order to cool theeffluent to about 110° F. and to recapture the heat for use elsewhere inthe process.

After passing through heat exchangers 106, the heavy effluent from firstdistillation column 300 will be transferred to a settling tank 400. Atthis stage, the effluent will comprise primarily bio-diesel (andsolvent) and glycerol. Glycerol is heavier than and not miscible inbio-diesel. With time, the phases will gravity separate. Most of theremaining high boiling point contaminants are more soluble in theglycerin phase and, accordingly, will predominate in the glycerin layer.After separation, each phase may be pumped off—the glycerol forsale/disposal and the bio-diesel for further treatment, as needed.Residency in settling tank 400 on the order of twenty-four hours isexpected to be sufficient to effect a substantially complete separationof bio-diesel from the glycerol.

Separation of the bio-diesel from the glycerol may be accelerated byusing a centrifuge 500, such as the disc centrifuge available from AlfaLaval, of Richmond, Virginia.

After the bio-diesel has been removed from the glycerol, the sulfurcontent in the bio-diesel will be on the order of 20 to 40 ppm. This canbe contrasted with sulfur levels on the order of 1000 ppm in thefeedstock. It will also be appreciated that most water soluble sulfurcontaminants that might have been present in the effluent from reactor200 will have been removed either with the light effluent fromdistillation column 300 or with the glycerol phase in separation. Themajority of any remaining sulfur contaminants are likely to be watermiscible polar compounds such as alkyl sulfates.

By passing the bio-diesel through a bed of adsorbent, such as aluminumsilicate, the majority of any remaining sulfur contaminants may becaptured. The resulting bio-diesel will have a sulfur content of between0 and 10 ppm, and well below 15 ppm in any event.

The bio-diesel may also be passed through a molecular sieve 600 such asthose available from W.R. Grace of Baltimore, Maryland to remove anyresidual water. This is essentially an insurance step, as distillationwill have already removed substantially all waters.

The bio-diesel is passed through a one micron filter 700, such as thoseavailable from AWC, Inc. of Mobile, Alabama. This ensures that the finalfuel product contains substantially no particulates, or at leastsubstantially nothing above a micron in size.

If bio-diesel is used as the solvent, there is no need to extract itfrom the finished product. If diesel is used as the solvent, it may ormay not be necessary to remove the diesel, depending upon the intendeduse of the end product. If diesel or another solvent needs to beremoved, 15 separation can be accomplished by cooling thebio-diesel/solvent mixture to a temperature approaching the gel point ofthe bio-diesel. The gel point of fuel produced by the current processwill vary depending upon the fatty acid composition of the feed stock.However, the gel point of most bio-diesel created using the processdescribed herein will be between 15° and 65° F. By comparison, the gelpoint of number two diesel is around −10° F. to 20° F. As the bio-dieseland solvent mixture approaches temperatures near the gel point of thebio-diesel—commonly in the range of 65° to 60° F.—the specific gravityof the bio-diesel will increase, and the bio-diesel will sink to thebottom of the tank. This will allow the solvent to be pumped off forreuse. The bio-diesel can be warmed or simply allowed to return toambient temperature, and its liquid properties will return. At thispoint the bio-diesel is ready for sale or use.

In operation, the foregoing process will yield bio-diesel having lessthan 15 ppm sulfur, essentially no water and will meet or exceedindustry fuel specification ASTM 6751-12. This may be obtained using nomore than about twenty-one percent alcohol by weight and typicallyalcohol quantities more on the order of about twelve to sixteen percentby weight. Total reaction time, from emulsification of the refinedstock, solvent, and alcohol through post-reaction distillation will takeabout 4.5 minutes.

It will be appreciated that the foregoing process may be operated on acontinuous, as opposed to a batch, basis. This will enhance efficiencysignificantly. In addition to simply allowing more bio-diesel to beproduced per unit time, the continuous process makes it possible toefficiently capture and reuse heat. This, in turn, will make the cost ofoperation significantly less expensive.

Example No. 1

A refined feedstock was treated according to the methods describedherein. The feedstock comprised about 50.7 percent by weight triolein (asymmetrical triglyceride typically present in olive oil); about 13.9percent by weight solvent in the form of methyl oleate (bio-diesel);about 8.0 percent water by weight; about 0.0073 percent by weight carbondisulfide and 0.0073 sodium sulfate. To this was added, about 27.3percent by weight methanol to form an 20 emulsion. All percentages aregiven with respect to the emulsion. The molar ratio of the methanol totriglycerides in the emulsion was about 15:1.

The emulsion was pressurized to about 2500 psig and heated to about 600°F. It was then passed through a reactor substantially as describedabove. Heat transfer media in the reactor was maintained at about 750°F. Pressure in the reaction lines was maintained at about 2500 psigthroughout the process.

The manifold was used to break the reaction lines in the reactor intotwo separate circuits, each circuit comprising seven reaction line coilsand containing about 350 feet of reaction line in each circuit. Theemulsion was separated into two streams, each of which was pumpedthrough one of the circuits at about 3.0 gallons per minute. Theemulsion remained in the reactor for about 4.5 minutes.

Post-reaction, the effluent comprised about 21.8 percent by weightmethanol; about 64.9 percent by weight methyl oleate (about 51% byweight was formed in the reactor and about 13.9% was carry-oversolvent); about 5.3 percent by weight glycerol; about 8.0 percent byweight water; about 0.0073 percent by weight carbon disulfide and about0.0073 percent by weight sodium sulfate. The effluent was subjected toflash distillation to remove the methanol, water and carbon disulfide;centrifugation to remove the glycerol; and filtration to remove thesodium sulfate. The resultant bio-diesel (methyl oleate) met the ASTM6751-12 fuel quality specifications for B100. Detailed results of thistesting are reported in FIG. 6A.

Example No. 2

A refined feedstock was treated according to the methods describedherein. The feedstock comprised about 10.3 percent by weight triolein(triglyceride); about 20.8 percent by weight diolein (diglyceride);about 10.8 percent by weight monoolein (monoglyceride); about 21.9percent by weight solvent in the form of methyl oleate (bio-diesel);about 13.2 percent water by weight; about 0.011 percent by weight carbondisulfide and about 0.011 sodium sulfate. To this was added, about 23.0percent by weight methanol to form an emulsion. All percentages aregiven with respect to the emulsion. The molar ratio of the methanol toglycerides in the emulsion was about 10:1.

The emulsion was pressurized to about 2500 psig and heated to about 600°F. It was then passed through a reactor substantially as describedabove. Heat transfer media in the reactor was maintained at about 750°F. Pressure in the reaction lines was maintained at about 2500 psigthroughout the process.

The manifold was used to break the reaction lines in the reactor intotwo separate circuits, each circuit comprising seven reaction line coilsand containing about 350 feet of reaction line in each circuit. Theemulsion was separated into two streams, each of which was pumpedthrough one of the circuits at about 3.25 gallons per minute. Theemulsion remained in the reactor for about 4.2 minutes.

Post-reaction, the effluent comprised about 18.7 percent by weightmethanol; about 61.2 percent by weight methyl oleate (about 40% byweight was formed in the reactor and about 21% was carry-over solvent);about 6.9 percent by weight glycerol; about 13.2 percent by weightwater; about 0.011 percent by weight carbon disulfide and about 0.011percent by weight sodium sulfate. The effluent was subjected to flashdistillation to remove the methanol, water and carbon disulfide;centrifugation to remove the glycerol; and filtration to remove thesodium sulfate. The resultant bio-diesel (methyl oleate) met the ASTM6751-12 fuel quality specifications for B100. Detailed results of thistesting are reported in 6B.

Example No. 3

A refined feedstock was treated according to the methods describedherein. The feedstock comprised about 6.2 percent by weight triolein(triglyceride); about 14.7 percent by weight diolein (diglyceride);about 21.6 percent by weight monoolein (monoglyceride); about 22 percentby weight solvent in the form of methyl oleate (bio-diesel); about 13.2percent water by weight; about 0.011 percent by weight carbon disulfideand about 0.011 sodium sulfate. To this was added, about 22.2 percent byweight methanol to form an emulsion. All percentages are given withrespect to the emulsion. The molar ratio of the methanol to glyceridesin the emulsion was about 8:1.

The emulsion was pressurized to about 2500 psig and heated to about 600°F. It was then passed through a reactor substantially as describedabove. Heat transfer media in the reactor was maintained at about 750°F. Pressure in the reaction lines was maintained at about 2500 psigthroughout the process.

The manifold was used to break the reaction lines in the reactor intotwo separate circuits, each circuit comprising seven reaction line coilsand containing about 350 feet of reaction line in each circuit. Theemulsion was separated into two streams, each of which was pumpedthrough one of the circuits at about 3.25 gallons per minute. Theemulsion remained in the reactor for about 4.2 minutes.

Post-reaction, the effluent comprised about 18.1 percent by weightmethanol; about 60.3 percent by weight methyl oleate (about 38.3% byweight was formed in the reactor and about 22% was carry-over solvent);about 8.4 percent by weight glycerol; about 13.2 percent by weightwater; about 0.011 percent by weight carbon disulfide and about 0.011percent by weight sodium sulfate. The effluent was subjected to flashdistillation to remove the methanol, water and 20 carbon disulfide;centrifugation to remove the glycerol; and filtration to remove thesodium sulfate. The resultant bio-diesel (methyl oleate) met the ASTM6751-12 fuel quality specifications for B100. Detailed results of thistesting are reported in FIG. 6C.

Example No. 4

A refined feedstock was treated according to the methods describedherein. The feedstock comprised about 2.0 percent by weight triolein(triglyceride); about 10.3 percent by weight diolein (diglyceride);about 10.6 percent by weight monoolein (monoglyceride); about 17.9percent oleic acid (free fatty acid); about 24.2 percent by weightsolvent in the form of methyl oleate (bio-diesel); about 14.4 percentwater by weight; about 0.013 percent by weight carbon disulfide andabout 0.013 sodium sulfate. To this was added, about 20.5 percent byweight methanol to form an emulsion. All percentages are given withrespect to the emulsion. The molar ratio of the methanol toglycerides/free fatty acids in the emulsion was about 6:1. The emulsionwas pressurized to about 2500 psig and heated to about 600° F. It wasthen passed through a reactor substantially as described above. Heattransfer media in the reactor was maintained at about 750° F. Pressurein the reaction lines was maintained at about 2500 psig throughout theprocess.

The manifold was used to break the reaction lines in the reactor intotwo separate circuits, each circuit comprising seven reaction line coilsand containing about 350 feet of reaction line in each circuit. Theemulsion was separated into two streams, each of which was pumpedthrough one of the circuits at about 3.25 gallons per minute. Theemulsion remained in the reactor for about 4.2 minutes.

Post-reaction, the effluent comprised about 16.2 percent by weightmethanol; about 63.7 percent by weight methyl oleate (about 39.7% byweight was formed in the reactor and about 24% was carry-over solvent);about 4.5 percent by weight glycerol; about 15.6 percent by weightwater; about 0.013 percent by weight carbon disulfide and about 0.013percent by weight sodium sulfate. The effluent was subjected to flashdistillation to remove the methanol, water and carbon disulfide;centrifugation to remove the glycerol; and filtration to remove thesodium sulfate. The resultant bio-diesel (methyl oleate) met the ASTM6751-12 fuel quality specifications for B100. Detailed results of thistesting are reported in FIG. 6D.

Example No. 5

A refined feedstock was treated according to the methods describedherein. The feedstock comprised about 9.0 percent by weight triolein(triglyceride); about 35.5 percent oleic acid (free fatty acid); about27 percent by weight solvent in the form of methyl oleate (bio-diesel);about 15.8 percent water by weight; about 0.014 percent by weight carbondisulfide and about 0.014 sodium sulfate. To this was added, about 12.5percent by weight methanol to form an emulsion. All percentages aregiven with respect to the emulsion. The molar ratio of the methanol toglycerides/free fatty acids in the emulsion was about 3:1.

The emulsion was pressurized to about 2500 psig and heated to about 600°F. It was then passed through a reactor substantially as describedabove. Heat transfer media in the reactor was maintained at about 750°F. Pressure in the reaction lines was maintained at about 2500 psigthroughout the process.

The manifold was used to break the reaction lines in the reactor intotwo separate circuits, each circuit comprising seven reaction line coilsand containing about 350 feet of reaction line in each circuit. Theemulsion was separated into two streams, each of which was pumpedthrough one of the circuits at about 3.5 gallons per minute. Theemulsion remained in the reactor for about 3.9 minutes.

Post-reaction, the effluent comprised about 7.5 percent by weightmethanol; about 73.5 percent by weight methyl oleate (about 46.5% byweight was formed in the reactor and about 27% was carry-over solvent);about 0.95 percent by weight glycerol; about 18 percent by weight water;about 0.014 percent by weight carbon disulfide and about 0.014 percentby weight sodium sulfate. The effluent was subjected to flashdistillation to remove the methanol, water and carbon disulfide;centrifugation to remove the glycerol; and filtration to remove thesodium sulfate. The resultant bio-diesel (methyl oleate) met the ASTM6751-12 fuel quality specifications for B100. Detailed results of thistesting are reported in FIG. 6E.

Although the preferred embodiment has been described, those skilled inthe art to which the present invention pertains will appreciate thatmodifications, changes, and improvements may be made without departingfrom the spirit of the invention defined by the following claims.

We claim:
 1. A reactor comprising: a substantially fluid tight tankcomprising an interior and an exterior; a heat transfer media positionedwithin said tank; a plurality of reaction lines positioned within saidtank, wherein said plurality of reaction lines are in thermalcommunication with said heat transfer media and wherein said pluralityof reaction lines are in fluid communication with one another and withsaid exterior of said tank; a manifold configured to regulate fluidcommunication between said plurality of reaction lines, wherein saidmanifold is configured to selectively allow fluid exiting a first ofsaid plurality of reaction lines to flow to a second of said pluralityof reaction lines or to divert fluid exiting said first of saidplurality of reaction lines away from said second of said plurality ofreaction lines, wherein said manifold is configured to divert a fluidhaving a density and exiting said first of said plurality of reactionlines out of said reactor if the density of the fluid has fallen by atleast about 1 pound per cubic foot; at least one means for heating saidheat transfer media; and at least one pump configured to drive reactantfluids through at least one of said plurality of reaction lines.
 2. Areactor according to claim 1 wherein said manifold is provided with atleast one sensor configured to measure a mass flow rate of said fluidflowing through said reactor.
 3. A reactor according to claim 1 furthercomprising at least one heat exchanger in thermal communication withsaid reactant fluids, whereby said fluids may be heated to a desiredtemperature prior to entering said plurality of reaction lines.
 4. Areactor according to claim 3 wherein said at least one pump isconfigured to pressurize said reactant fluids to a desired pressureprior to entering said plurality of reaction lines.
 5. A reactoraccording to claim 4 wherein said plurality of reaction lines areconfigured to maintain said reactant fluids at about said desiredpressure.
 6. A reactor according to claim 5 said plurality of reactionlines are in fluid communication with at least one back pressure valve.7. A reactor according to claim 5 wherein said plurality of reactionlines are configured to maintain substantially non-laminar flow of saidreactant fluids.
 8. A reactor according to claim 7 wherein said at leastone of said plurality of reaction lines has a spiral configuration.
 9. Areactor according to claim 1 further comprising a reservoir in fluidcommunication with said tank, wherein said reservoir contains an excessof said heat transfer media.
 10. A reactor according to claim 9 whereinsaid reservoir is at least about twenty-five percent the volume of saidtank.
 11. A reactor according to claim 9 further comprising at least onecirculation pump, said at least one circulation pump configured to mixsaid heat transfer media within said tank and said reservoir, wherebysaid heat transfer media in said tank and said reservoir may bemaintained at about the same temperature.
 12. A reactor according toclaim 9 further comprising at least one heat exchanger in thermalcommunication with said reactant fluids, whereby said fluids may beheated to a desired temperature prior to entering said plurality ofreaction lines wherein said at least one heat exchanger is positioned insaid reservoir.
 13. A reactor according to claim 12 wherein said atleast one heat exchanger is substantially surrounded by said heattransfer media.
 14. A reactor according to claim 13 wherein said heattransfer media comprises molten salt.
 15. A reactor according to claim14 wherein said heat transfer media is selected from the groupconsisting of potassium nitrate, sodium nitrite, sodium nitrate, andmixtures thereof.
 16. A reactor according to claim 1 wherein said atleast one pump is configured to pressurize said reactant fluids to adesired pressure prior to entering said plurality of reaction lines. 17.A reactor according to claim 16 wherein said plurality of reaction linesare configured to maintain said reactant fluids at about said desiredpressure.
 18. A reactor according to claim 17 wherein said plurality ofreaction lines are configured to maintain substantially non-laminar flowof said reactant fluids.
 19. A reactor comprising: a substantially fluidtight tank comprising an interior and an exterior; a heat transfer mediapositioned within said tank; a plurality of reaction lines positionedwithin said tank, wherein said plurality of reaction lines are inthermal communication with said heat transfer media and wherein saidplurality of reaction lines are in fluid communication with one anotherand with said exterior of said tank; a manifold configured to regulatefluid communication between said plurality of reaction lines, whereinsaid manifold is configured to selectively allow fluid exiting a firstof said plurality of reaction lines to flow to a second of saidplurality of reaction lines or to divert fluid exiting said first ofsaid plurality of reaction lines away from said second of said pluralityof reaction lines; wherein said manifold is provided with at least onesensor configured to measure a mass flow rate of fluid flowing throughsaid reactor, said fluid having a density, and wherein said manifold isconfigured to divert fluid exiting said first of said plurality ofreaction lines away from said second of said plurality of reaction linesif the density of the fluid has fallen by at least about 1 pound percubic foot; at least one means for heating said heat transfer media; andat least one pump configured to drive reactant fluids through at leastone of said plurality of reaction lines.
 20. A reactor according toclaim 19 wherein said manifold is configured to divert fluid exitingsaid first of said plurality of reaction lines out of said reactor ifthe density of the fluid has fallen by at least about 1 pound per cubicfoot.